The present invention relates to methods and compositions for inhibiting the corrosion of ferrous metals by aqueous mediums, particularly brines. More particularly, the present invention is related to reducing the corrosion of iron and steel casing, tubing and other ferrous, subterranean well structural parts exposed to brines used as completion, workover, packer fluids and other well servicing fluids.
In well servicing operations, clear, solids free completion, workover and packer fluids, e.g. brines, are utilized for various purposes, especially where a relative dense fluid is desired. While alkali metal salt brines may be employed in such applications, it is more common to employ brines of salts such as calcium chloride, calcium bromide, zinc chloride, zinc bromide, etc. because they provide well servicing fluids of greater specific gravity. It is well known that such brines are corrosive to ferrous metal goods in the well bore even in the absence of substantial oxygen. The problem is further accentuated by the fact that well bore temperatures commonly exceed 120.degree. C., increasing the rate of corrosion. A particular problem regarding the corrosiveness of such brines occurs when they are used as packer fluids in which case they remain substantially static in the well bore and in continuous, relatively long duration contact with subterraneous ferrous metal well components.
British Pat. No. 2,027,686 discloses a method of inhibiting the corrosion of ferrous metals exposed to aqueous brines by including in the brine an effective amount of a sulfur compound wherein the oxidation state of the sulfur is zero or less, a particularly preferred sulfur compound being ammonium thiocyanate.